More salt

Q.Could a person's hair in fact turn white overnight from fright, as Marie Antoinette's and Thomas More's were said to have done just hours before their execution? ­V. Sassoon

A. Overnight graying or whitening has been reported for centuries, but the two historic cases cited are disputed. What does modern science say? Will a strong scare really de-color the hair? No and yes. The "no" is that hairs don't suddenly just lose their pigment. The "yes" is that a strong emotional shock can cause a rapid loss of large amounts of hair, and if this is mostly the pepper (pigment-bearing locks) of a salt-and-pepper head, then the salt shall remain.

Losing mostly pepper is indeed possible with a condition termed alopecia areata. So for these folks, a strong shock or life crisis can leave them with an apparent sudden shock of whiter hair.

Q. How do stealth aircraft stay "invisible" to radar? Don't cell phones today make this just a bit trickier? ­D. Rumsfeld

A. Look at a photo of an F-117A Nighthawk, D., and you'll see a strange, bat-like plane with skinny flat panels that lie almost totally horizontal and with virtually no part of the craft forming a vertical face or wall to reflect radar signals back to the station, say David Halliday et al. in Fundamentals of Physics. What reflections there are off low-angled surfaces– go skyward or groundward, harmlessly.

Of course, stealth aircraft also absorb microwaves, in effect becoming "black" to radar, says UVA's Louis A. Bloomfield in How Things Work: The Physics of Everyday Life.

"Just as you can't see a black bat against the night sky by shining a flashlight at it, you can't see a stealth aircraft against the night sky by shining microwaves (radar) at it," he writes.

But what if you could shine thousands of flashlights into the sky and scanned from above to see where the light wasn't coming through? Little dark silhouettes of bats would now appear, rendering them very visible. In the same way, cell phones and phone towers today are bathing the sky with microwaves, and any microwave-absorbing craft becomes visible from above as flying microwave shadows.

"This points out that invisibility is never perfect, and excellent camouflage in one situation may be terrible in another."

Q.Bugged reader asks, What is the source of those annoying fruit flies hovering around the fruit bowl? Do they arrive as stowaways on fruit from the grocery store? ­-Chaquita B.

A. No, actually they disdain unripe store fruit, says Discovery.com. They come into the house from the great outdoors "when they smell your peaches rolling across the ripeness line."

Once Drosophila melanogaster finds ripening fruit, eggs will instantly follow, and 30 hours later, larvae– hundreds of them. Within days, they will hatch and renew the cycle.

And it doesn't take much to sustain them– slime in a sink drain, a sour mop, damp floor crumbs, alcohol fumes!

A nuisance, true, Chaquita, but fruit flies deserve special mention in the helper-bugs Hall of Fame. Easy to manage and prodigiously reproductive– a generation every 8-10 days, allowing fast-forward mutational testing. By 1910, fruit flies had become the perfect genetics lab animal, says University of Illinois entomologist May Berenbaum in Bugs in the System: Insects and their Impact on Human Affairs.

From early principles of heredity to gene therapy to mapping of the genome, the whole genetics engineering revolution "effectively originated almost a century ago with rotten bananas and the flies that love them."